If you're flying, taking the train, or otherwise heading somewhere the weather could be different, visiting isitraining.in could be a day saver. Add a slash and your intended city after the URL, and you get your answer to "Is it raining?"

So entering isitraining.in/chicago gets you the yes/no answer, and some basic weather, on that famed windy city. Some cities or towns may require adding a state or country after the name—isitraining.in/syracuse-italy and isitraining.in/syracuse-ny are two very different places, after all. Handy stuff, when it's available. At the moment, their servers seem to be taking a hit, so perhaps a bookmark is required for later perusal.

On a similar note, you may also be interested in previously mentionedUmbrella Today?, a webapp that sends email, SMS, or push (on iOS) reminders only on days you need an umbrella where you live.